This invention relates to a method for installing sleeved fasteners though multiple layers to achieve a high interference fit of the sleeved fasteners within their respective holes in the layers. More particularly, this invention relates in one embodiment to a method for installing fasteners in which the sleeves for the fasteners are initially inserted in a sliding fit into the holes followed by a high interference fit forcing of the fastener into the sleeve. Still more particularly, this invention relates to a method for installing sleeve fasteners in which the sleeves have uniquely formed radii at specified edges in the holes to stress coin these edges when the fasteners are inserted in the interference fit within the sleeves.
Normal practice for fastening multiple layers together is to clamp up the layers, drill holes, and then insert some type of fastener into the holes and thereby secure the layers together. The fasteners are usually inserted in a net or sliding fit in the receiving holes in the layers. For many applications this will be sufficient. However, when the assembled structure is subjected to cyclic loading, the looseness of the fit of the fasteners within their holes will result in continual working of the fasteners within their holes. This in turn leads to fretting corrosion and fatigue failure of either the fastener or the surrounding region of the layers adjacent a particular hole.
However, it is known that the utilization of a high interference fit of the fastener of the hole can effectively prevent the majority of this fretting corrosion due to cyclic loading of the assembled structure. In many cases an oversized fastener will be driven directly into the receiving hole in the layers. In other cases the use of a sleeve which is slipped into the hole in a net or sliding fit followed by the drive-in of the oversized fastener is utilized. For these last systems, see for example U.S. Pat. No. 3,820,297 for an interference fit blind fastener and also U.S. Pat. No. 4,244,661 for a fastener means and joint for laminates, assigned to the assignee of this invention, McDonnell Douglas Corporation.
Nevertheless, there remains a need for a fastener system which combines the concept of interference fit sleeved fasteners with the added benefit of stress coining and total hole filling at the edges of the hole.